Some battery chargers used in applications such as in charging automotive batteries and the like include means for supplying a high charging current to the battery, for example, 40 amps to provide for rapid charging of the battery. They may include means for reducing the charge being supplied to the battery once the voltage of the battery has reached a predetermined voltage. For example, in a conventional 12 volt automatic battery charger, the charge is reduced to 0.1 amps or less once the voltage of the battery reaches approximately 14.4 volts. The reduced charge of 0.1 amps or less is then continuously supplied to the battery to maintain the charge on the battery. In operation of these battery chargers, if the battery charger continues to supply a low current charge to the battery for extended periods of time, the water in the battery will be converted to hydrogen and oxygen which is dissipated from the battery causing damage to the battery. In addition, if the battery charger continues to supply a low current charge to the battery for extended periods of time, the grids of the battery being charged will corrode at an accelerated pace, thereby causing the battery to fail prematurely. On the other hand, if the battery is left uncharged for a long period of time, self discharge of the battery will cause the active material of the battery to sulfate, thus also causing irreversible damage to the battery.
Some battery chargers of the type including means for sensing the state of charge of a battery and interrupting the charging cycle when the battery has been fully charged further include means for continuing to monitor the state of charge of the battery and for automatically restarting the supply of charging current to the battery when the battery's state of charge is below full charge.
Another type of battery charger supplies only relatively small charges to a battery, for example a charge at the rate of 10 amps, and includes means for sensing the charge of the battery and means for shutting off the charging current to the battery once the voltage of the battery reaches a predetermined voltage, for example 14.4 volts. The battery charger will then continue to sense the charge of the battery and if that voltage falls below a predetermined voltage, the charger will once again supply a charging current to the battery until the voltage of the battery is raised to 14.4 volts, and is again interrupted.
In other battery chargers, means are provided for supplying a charge to the battery at a relatively high rate of charge, such as at approximately 40 amps, or alternatively at a lower rate such as at 10 to 15 amps. These battery chargers commonly include a switch or control permitting the operator to select the operating mode of the battery charger such that it operates at either a high current rate or at a lower current of approximately 10 to 15 amps.
Other battery chargers have included means for charging the battery at a high rate of charge and alternative means for charging the battery at a lower rate, and further including means for timing the selected rate of charge. In these chargers the battery is then charged at the selected rate of charge until the timer turns off the charger.